high-Mn Austenitic Steel Research Articles

Enhancing dry sliding wear resistance of high-Mn austenitic steel by adding N

In this study, the wear resistance of two high-Mn austenitic steels, i.e., Fe−18.5Mn−7Cr−0.6C and Fe−18.5Mn−7Cr−0.6C−0.21N was tested in dry sliding friction on a disc friction and wear testing machine (MMU-5G). The wear behavior and microstructure evolution of the two tested steels were investigated. The results revealed that adding N enhanced the wear resistance of high-Mn austenitic steel due to the synergistic effects of hardness, wear hardening, and oxide layer. Interstitial N atoms increased the matrix hardness and decreased the stacking fault energy (SFE). The lower SFE facilitated wear hardening, and the active mechanical twins along with the higher dislocation density induced the formation of a thicker nanocrystalline layer with finer grains. The nanocrystalline layer with higher surface activity promoted the adsorption of a protective oxide layer. These factors decreased the surface roughness, coefficient of friction (COF), and wear rate of N-alloyed high-Mn austenitic steel. This study provided valuable insights into the application of N-alloyed high-Mn austenitic steels under dry sliding friction conditions.

The adverse effect of grain refinement on hydrogen embrittlement in a high Mn austenitic steel

This study presents a novel observation wherein the reduction in grain size (GS) from 20 μm to 1 μm in austenitic steel adversely affects hydrogen embrittlement (HE). The findings indicate an increase in total absorbed hydrogen with grain refinement when subjected to cathodic hydrogen charging. The results demonstrate that even with grain refinement to 1 μm, the primary mode of hydrogen damage remains intergranular, with a significant increase in relative elongation loss (REL%). This phenomenon is attributed to the early nucleation of intergranular hydrogen-induced cracks (HICs) and the accelerated propagation rates of HICs, leading to local stress increments and rapid alloy failure. The accelerated development of HICs is ascribed to the impact of grain refinement on intensified normal stress exerted on grain boundary planes, as well as the suppression of ε-martensite and its positive effect on crack arresting. Besides the enhanced degradation rate of the hydrogen-affected area (HAA) due to grain refinement, the higher ratio of HAA to the entire cross-sectional area was identified as a crucial factor contributing to rapid failure and the inverse effect of grain refinement on HE resistance.

Influence of hydrogen on deformation and embrittlement mechanisms in a high Mn austenitic steel: In-Situ neutron diffraction and diffraction line profile analysis

Austenitic steels have relatively high resistance to hydrogen embrittlement and play a critical role in hydrogen service applications. In particular, high Mn austenitic steels are considered economically viable alloy alternatives for these applications. The current study employed in-situ and ex-situ neutron diffraction techniques combined with diffraction line profile analysis (DLPA) to investigate the influence of hydrogen on deformation and embrittlement mechanisms in a high Mn (approximately 30 wt pct) austenitic steel. Investigation using both neutron diffraction and electron backscatter diffraction revealed the presence of extensive deformation twins and stacking faults within the steel microstructure after tensile deformation in the non-charged condition. These microstructural features suggest planar deformation behavior, which is expected from the relatively low stacking fault energy (SFE) of the alloy (approximately 29 mJ/m2). Hydrogen pre-charging resulted in apparent increases in both dislocations and stacking faults, contributing to macroscopic hardening and embrittlement mechanisms. Overall, numerical parameters obtained through neutron DLPA were used to elucidate the underlying mechanisms associated with hydrogen effects on the mechanical behavior, i.e. macroscopic strengthening, strain hardening rate, and embrittlement.

Effect of final rolling temperature on the microstructure and properties of high-manganese austenitic low-temperature steel

The effect of final rolling temperature ranging from 962 to 696 °C on as-rolled high-Mn austenitic low-temperature steel was investigated using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The microstructure of the experimental steel remained austenite without suffering ferrite phase transformation, even when produced with a final rolling temperature as low as 696 °C. A decrease in the final rolling temperature of the steel was accompanied by a decrease in grain size from 20.2 to 6.0 μm, accompanied by an increase in dislocation density from 3.01 × 1014 to 10.9 × 1014 m−2. In addition, M23C6 carbides precipitated at the grain boundaries when the final rolling temperature was below 782 °C. Grain refinement and increased dislocation density significantly enhanced the strength of the material. However, an increase in the intragranular dislocation density compromised grain deformation ability. Moreover, the precipitation of M23C6 reduced the plasticity and toughness of the material. Considering the balance between yield strength and low-temperature toughness, the optimal final rolling temperature was 898 °C; this produced a material with a yield strength of approximately 507 MPa and a low-temperature impact energy absorption of approximately 143 J.

Mechanism of DSA effect correlating to the macroscopic PLC banding in high-Mn austenitic steel

Mechanism of dynamic strain aging (DSA) effect in high-Mn austenitic steel, and its correlation with the Portevin-Le Chatelier (PLC) banding, was elucidated using the in-situ synchrotron XRD measurement and digital image correlation (DIC) method during tensile test. The average dislocation velocity beyond the PLC band ranged from 10−2 to 10−1 nm/s, while reached to the order of 10° nm/s within the PLC band. In comparison, carbon diffusivity was significantly lower, allowing carbon atoms to diffuse only from 10−7 to10−9 nm in one second. The findings indicate that dislocations beyond the advancing PLC band were pinned by nearby carbon atoms, while dislocations within the PLC band became de-pinned from the carbons. Such localized pinning and de-pinning of dislocations occurred sequentially during deformation, appearing as the propagation of PLC bands in macroscopic scale.

Key role of gradient-nanostructure and extremely thin amorphous passive film on tribocorrosion behavior of a novel Cr+N alloyed high-Mn austenitic steel

High manganese steel is influenced by the combined effects of corrosion and wear during service under specific conditions, resulting in components with shortened service life. Under harsh service environments, newly developed Cr+N alloyed austenitic high manganese steel (Mn18Cr7C0.6N0.2 steel) as a new type of railway steel has shown promising results. Herein, the tribocorrosion behaviors of Mn18Cr7C0.6N0.2 and Mn13C1.1 steels in artificial acid rain were studied using electrochemical methods, field emission scanning electron microscope (FE-SEM), focused ion beam scanning electron microscopy (FIB-SEM), scanning transmission electron microscopemicroscopy energy dispersive X-ray spectroscopy (STEM-EDS), and high resolution transmission electron microscopy (HR-TEM). The results showed the formation of passive film and gradient-nanostructure on surfaces of both test steels during tribocorrosion. A dense and tightly adhering amorphous passive film was formed on Mn18Cr7C0.6N0.2 steel surface with a superior blocking effect toward invasive ions. The high strain resistance and plasticity of the Mn18Cr7C0.6N0.2 steel resulted in an intact gradient-nanostructure, suitable for obtaining high surface hardness and maintaining the toughness of the matrix, contribute to providing high wear resistance. The oxide film on the Mn13C1.1 steel surface comprised crystal α-FeOOH. Vortex cracks formed in its gradient structure due to strain localization. Meanwhile, the relatively poor corrosion protection ability and vortex cracks of its gradient-nanostructure prevented it from maintaining interface integrity of the gradient nanostructure, resulting in inferior tribocorrosion resistance. In artificial acid rain, the new type of Cr+N alloyed Mn18Cr7C0.6N0.2 steel exhibited higher tribocorrosion resistance than traditional high manganese steel, promising for use as an excellent wear-resistant material under corrosive environments.

Adding N to enhance low-cycle fatigue properties of high-Mn austenitic steel

This study comparatively investigated the low-cycle fatigue properties and microstructure of two high-Mn austenitic steels, Fe−18.5Mn–7Cr−0.6C and Fe−18.5Mn–7Cr−0.6C−0.21 N. The results revealed that adding N promoted the dislocation planar slip during cyclic deformation in high-Mn austenitic steel, due to the presence of Cr–N short-range ordering (SRO) and the decrease of stacking fault energy (SFE). With an increased number of cycles, the planar slip characteristics of the N-containing high-Mn austenitic steel led to a rapid decrease in effective stress, which promoted cyclic softening. Moreover, adding N increased the fatigue life of high-Mn austenitic steel, by enhancing the fatigue strength, reducing the plastic damage accumulation, and inhibiting the fatigue crack propagation. This study provided a valuable reference for the practical applications of N-alloyed high-Mn austenitic steel.

Effect of N on microstructure evolution and strain hardening of high-Mn austenitic steel during tensile deformation

The present study investigated the microstructure evolution and strain hardening of two types of high-Mn austenitic steels, i.e., Fe−18.5Mn–7Cr−0.6C (00 N) and Fe−18.5Mn–7Cr−0.6C−0.21 N (21 N), during tensile deformation. The results revealed that the addition of N increased the yield and tensile strength of high-Mn austenitic steel with almost no loss of elongation. The strain hardening of the 00 N and 21 N steels was closely related to the microstructure evolution. At the initial tensile deformation stage, dislocation slip was the dominant deformation mechanism of the two test steels. Due to the addition of N, the dislocation cross-slip in the 21 N steel was suppressed, leading to a higher strain hardening rate. With the increase of true strain, the mechanical twins became active. At a true strain of 0.18, a unique network structure of mechanical twins and dislocation cells was formed in the 00 N steel, and the thickness and spacing of mechanical twins were lower, which increased the resistance of dislocation motion and made its strain hardening rate slightly higher than that of the 21 N steel. However, at a true strain of 0.37, the thickness and spacing of mechanical twins in the 21 N steel decreased rapidly, which increased the difficulty of dislocation movement, resulting in a higher strain hardening rate than that of the 00 N steel. In short, the increased resistance of dislocation motion was the fundamental reason for the enhanced strain hardening rate, rather than mechanical twins.

Mechanism of simultaneous increase of strength and ductility with grain refinement in Si-added high-Mn austenitic steel

We systematically investigated the effect of grain refinement on mechanical properties and fracture behavior of Si-added high-Mn austenitic steel. A 22Mn-0.6C–3Si steel (wt. %) with single-phase FCC structure was investigated in the present study. By applying high pressure torsion (HPT) and subsequent annealing process, specimens with fully recrystallized microstructures having various mean grain sizes ranging from 0.9 μm to 113 μm were obtained. The present steel exhibited a unique mechanical behavior that both strength and ductility simultaneously improved with grain refinement. Coarse-grained (dmean = 113 μm) and medium-grained (dmean = 13 μm) specimens fractured before reaching the plastic instability condition, whereas ultrafine-grained specimen (dmean = 0.9 μm) fractured after satisfying the plastic instability condition. Deformation microstructures of tensile-fractured specimens were investigated by using EBSD phase map. Obtained results revealed that the fraction of deformation induced ε-martensite significantly decreased with the grain refinement. At the same time, fracture surfaces of the different grain-sized specimens showed that the fraction of the fracture surfaces having step-like ridge pattern decreased with the grain refinement. Micro-cracks were observed to characterize a crack initiation site, and it was found that micro-cracks formed and propagated along the prior austenite grain boundaries where ε-martensite impinged. By applying the fracture surface topography analysis (FRASTA) to the tensile-fractured specimens, it was revealed that the crack initiated from the step-like ridge pattern, where each step was considered to be ε-martensite plate. The results consistently suggested that the step-like ridge pattern was grain boundary fracture surface related to ε-martensite, and grain refinement suppressed the ε-martensitic transformation and avoid the fracture before reaching the plastic instability condition, leading to the enhanced ductility as well as the high strength.

Effect of Grain Size on the Local Deformation Behavior Associated with the Discontinuous Yielding in a High Mn Austenitic Steel

Effect of Grain Size on the Local Deformation Behavior Associated with the Discontinuous Yielding in a High Mn Austenitic Steel

Characterization of Crack Growth Acceleration of V-added Precipitation-strengthened High-Mn Austenitic Steel in High-pressure Gaseous Hydrogen Environment

Characterization of Crack Growth Acceleration of V-added Precipitation-strengthened High-Mn Austenitic Steel in High-pressure Gaseous Hydrogen Environment

Effect of N on hot deformation behavior of high-Mn austenitic steel

The present study dealt with the hot compression deformation behavior of Fe−18.5Mn–7Cr−0.6C and Fe−18.5Mn–7Cr−0.6C−0.21 N high-Mn austenitic steels within a temperature range of 900–1200 °C, a strain rate range of 0.01–5 s−1, and a true strain of 0.7. The accurate constitutive equations were established according to their flow curves, and the deformation microstructures were also analyzed. The results revealed that the dominant softening mechanism for the two test steels without substantial peak stress (higher Zenger-Holloman parameter values) could also be dynamic recrystallization (DRX) rather than dynamic recovery (DRV). The addition of N enhanced the strain rate sensitivity of high-Mn austenitic steel at low temperatures and high strain rates. Furthermore, the addition of N increased the high temperature strength and hot deformation activation energy (Q) of high-Mn austenitic steel. Moreover, the addition of N could also increase the DRX volume fraction and refine the DRX grain size of high-Mn austenitic steel.

Dynamic recrystallization behavior and microstructure evolution of high-Mn austenitic steel for application in a liquefied natural gas carrier

The hot-working behavior of high-Mn austenitic steel for liquefied natural gas carriers at the deformation temperature in the range of 1073–1273 K and the strain rate in the range of 0.01–10 s−1 was studied on a Gleeble-3800 thermomechanical simulator using a compression test. Electron backscatter diffraction was used to study the microstructure after deformation. Under each deformation condition, a peak stress appears in the stress-strain curve, which conforms to traditional dynamic recrystallization hot-working flow stress curves. A hyperbolic sine-law-type constitutive equation was established to predict the peak stress. The thermal deformation activation energy was 414.19 kJ/mol, and the stress index n was 4.94. The texture of the deformed grains consisted of strong <110> and weak <100> fibers along the compression direction. The main recrystallization mechanism was discontinuous dynamic recrystallization. The grain size of the discontinuous dynamic recrystallization grains tended to increase with increasing deformation temperature or decreasing strain rate. Processing maps were drawn based on the dynamic material model. At high deformation temperatures, the power consumption factor of dynamic recovery was greater than that of dynamic recrystallization, whereas at low deformation temperatures, the power consumption factor of discontinuous dynamic recrystallization was greater than that of dynamic recovery. There are two flow instability regions in the processing maps, 1243–1273 K/1-10 s−1 and 1073–1203 K/0.05–10 s−1. The formation of a ‘necklace microstructure’ was the main cause of deformation instability. The optimized process parameters for industrial production were 1243–1273 K/1-10 s−1.

Temperature dependency of hydrogen embrittlement resistance of austenitic Fe–24Mn–3Cr-0.5Cu-0.47C steel

Currently, austenitic stainless steel has been used as a tank material for liquid hydrogen storage. However, in this study, the resistance to hydrogen embrittlement (HE) of austenitic Fe–24Mn–3Cr-0.5Cu-0.47C steel was investigated at a wide temperature range from 300 K to 20 K through slow strain rate tensile tests, aiming to explore the possibility of Fe-high Mn steel as an alternative material. To date, there are few papers on the HE resistance of austenitic high Mn steel, especially at cryogenic temperatures. The HE resistance of the high Mn steel was compared to that of austenitic 304 stainless steel (STS 304). The HE resistance of the high Mn steel was continuously enhanced with decreasing tensile temperature from 300 K to 77 K, despite the occurrence of mechanical twinning due to the significant reduction in H diffusion. However, the HE resistance slightly decreased again at 20 K, primarily due to cracking induced by dislocations with an edge component. Although both the high Mn steel and STS 304 had similar resistance to HE in the temperature range of 123 K–20 K, the high Mn steel demonstrated superior resistance to HE at the temperature range of 123 K–300 K. This indicates that the strain-induced α′-martensitic transformation occurring in STS 304 during tensile deformation in that temperature range is more detrimental to the HE resistance compared to the mechanical twinning occurring in the high Mn steel.

In-situ investigation of the interaction between hydrogen and stacking faults in a bulk austenitic steel

The interaction between hydrogen (H) atoms and various microstructural defects remains a key to understand the H-induced damage and the subsequent premature failure of high-strength metallic materials. Previous studies on this subject are mainly focused on the in-situ probing of dislocations in a thin foil placed in an environmental transmission electron microscopy (TEM) cell. Here, a three-point bending test coupled with electron channeling contrast imaging (ECCI) has been applied to investigate the interaction of H with stacking faults (SFs) in a bulk high Mn austenitic steel. The expansion of some SFs, in terms of one partial dislocation movement within a partial dislocation pair, was observed on the H pre-charged sample when kept at a constant loading (i.e., a continuous H migration and likely build-up close to the pre-prepared notch tip). A temporal-resolved cross-correlation EBSD (CC-EBSD) measurement shows that the migration of H towards the notch tip region has a minor effect on the internal stress evolution. However, the local shear modulus (μ) and stacking fault energy (γSF) can be reduced by a local H segregation. Further theoretical calculation of SF ribbon width indicates that the reduction of μ by H results in the shrinkage of SF, while the H-induced reduction of γSF results in SF expansion at a lower resolved shear stress. The observed expansion of SF ribbons can be interrupted by a combined reduction of both μ and γSF due to H.

Cryogenic impact fracture behavior of a high-Mn austenitic steel using electron backscatter diffraction and neutron Bragg-edge transmission imaging

A unique impact fracture behavior is found in a high-Mn austenitic steel (24Mn–4Cr-0.4C-0.3Cu) in this work. The steel exhibits concurrent twinning-induced plasticity (TWIP) effect and the transformation-induced plasticity (TRIP) effect. By analyzing the load-deflection curves recorded during Charpy impact testing, the resistance to crack initiation and propagation is quantified from the absorbed energy. The high-Mn steel demonstrates good resistance to crack initiation at 273 K and 77 K. However, as the temperature decreases from 273 K to 77 K, there is an accelerated transition from stable crack growth to unstable crack growth during impact, resulting in the deterioration of resistance to crack propagation. The plastic deformation of the impact-tested samples, especially in the region close to the crack-path profile was quantitatively analyzed using neutron Bragg-edge transmission (BET) imaging. The deformation zones, divided by using the width of the 200 Bragg edge, exhibit good agreement with the impact absorbed energy characteristics obtained from dynamic load-deflection curves. Moreover, the unstable growth transition point was roughly determined on the impact-tested sample. Then, the electron backscatter diffraction (EBSD) technique is employed to examine the deformation microstructure along the crack-path in the impact-tested samples. The results revealed the dual roles of TRIP effect in impact toughness of the high-Mn steel. On one hand, the TRIP effect plays a positive role in improving resistance to crack initiation and propagation. On the other hand, the excessive accumulation of brittle ε/α՛-martensite caused by the enhanced TRIP effect at 77 K leads to quasi-cleavage fracture, thereby playing a negative role. Finally, we discussed the prominent toughening mechanisms associated with the TWIP and TRIP effects, which greatly impact the impact fracture behavior.

Study on hot workability of a novel Cr + N alloyed high-Mn austenitic steel

The hot deformation behaviors of a novel Cr + N alloyed high-Mn austenitic steel, namely 60Mn18Cr7N steel, and a traditional one, namely 120Mn13 steel, were comparatively investigated at a temperature range of 1173–1473 K and strain rate range of 0.001–1 s−1 using a single-pass hot compression test. The results indicate that the presence of additional alloying elements in the 60Mn18Cr7N steel leading to a higher flow stress during hot deformation. To better understand the hot deformation behavior and determine the optimal forging treatment region, constitutive models based on the Arrhenius equation and processing maps utilizing strain rate sensitivity (m) were employed. The deformation activation energy of the 60Mn18Cr7N steel was found to be significantly higher than that of the 120Mn13 steel. By analyzing the deformation microstructure and processing map, the optimal processing domain for the 120Mn13 steel was identified within a temperature range of 1373–1473 K and strain rate range of 0.1–1 s−1, while higher temperature or strain was required for the 60Mn18Cr7N steel to achieve significant recrystallization.

The influence of recrystallization annealing time on high cycle fatigue behavior of high-Mn austenitic steel at 77 K

Three high manganese austenitic steels were prepared by different recrystallization annealing time (0, 32, and 128 min) to investigate the effect of recrystallization annealing time on high-cycle fatigue behavior at 77 K. The microstructure was characterized by means of quasi in situ scanning electron microscope (SEM). When fatigue life is about 5.0 × 106 loading cycles, the fatigue strength at 77 K increases from 512 MPa to 625 MPa with the decrease in recrystallization annealing time (RAT). Decrease in RAT leads to grain refinement and the increase in density of dislocation. Grain refinement can delay crack initiation, prevent crack propagation, and hardly hinders the formation of deformation twins. In addition, it is surprising that the grain refinement and the increase in dislocation density promote the formation of nanoscale voids, which leads to stress relaxation and thus improve the fatigue performance.

Study on the Novel High Manganese Austenitic Steel Welded Joints by Arc Welding for Cryogenic Applications of LNG Tanks

The novel high-Mn austenitic steel is becoming a promising steel for cryogenic applications of LNG tanks. The welded joints take a critical role in cryogenic service for storage tanks. In this work, we developed well-matched high-Mn welding consumables and prepared the welded joints by shielded metal arc welding (SMAW), submerged arc welding (SAW) and gas tungsten arc welding (GTAW). The detailed welding parameters were proposed first, then the welding quality, mechanical properties, and microstructure were investigated. The results show that good welding quality, excellent mechanical properties, and stable levels of mechanical properties were obtained for high-Mn steel welded joints using similar welding consumables, the solid core of electrodes, and solid welding wires. Notably, the lowest cryogenic absorbed energy was found at 5 mm away from the fusion line rather than at the fusion line. The hardness of the welded joints was detected to be less than 280 HV due to the whole austenitic microstructure.

Achieving superior cryogenic impact toughness and sufficient tensile properties in a novel high-Mn austenitic steel weld metal via cerium addition

The microstructure and mechanical properties of the novel cryogenic high-Mn austenitic steel weld metals with different cerium (Ce) contents were investigated via electron back-scattered diffraction, scanning and spherical aberration-corrected transmission electron microscopy, and cryogenic impact and tensile test. The results indicated that the crystallographic grain size was significantly refined, and the relative frequency of high-angle grain boundaries increased with the increase of Ce content. Ce element addition could modify the main inclusions from irregular Al2O3 into regular Ce-containing inclusions. Meanwhile, the inclusions gradually became fine and dispersed, and the volume fraction of inclusions decreased with the increase of Ce content from 0 to 870 ppm. The increase of Ce content continuously improved cryogenic impact toughness from 82 J to 116 J, and yield strength, tensile strength and total elongation all increased to different degrees. We found that in addition to the beneficial changes in inclusion modification, grain refinement and increase in the proportion of high-angle grain boundaries, the solid solution of Ce also played a crucial role in the mechanical properties.